1. Field of the Invention
The invention is directed to a magnetic resonance imaging apparatus of the type having a reception antenna which receives high-frequency magnetic resonance signals from an examination subject, a high-frequency receiver connected to the reception antenna which demodulates the high-frequency magnetic resonance signals and which supplies samples of the demodulated magnetic resonance signals, to a signal processing unit, the signal processing unit allocating the samples to a spatial frequency space.
2. Description of the Prior Art
A magnetic resonance imaging apparatus of the type generally described above is disclosed in European Application 0 076 054. For generating an anatomical image from signals obtained from an examination region of the subject, the echo signals received after an excitation of the nuclear spins in the subject are allocated to a spatial frequency space dependent on various magnetic field gradients which are superimposed on a basic magnetic field, in which the subject is disposed. The spatial frequency space is also known as k-space. If only a single-slice tomogram is to be reconstructed, it is sufficient to occupy a single plane in the spatial frequency space, in which case the spatial frequency space becomes a signal k-plane.
Under unfavorable circumstances, stripe-like artifacts can appear in the reconstructed tomograms. It has now been found that such artifacts are caused by disturbances which are picked up via the reception channel, including the reception antenna, even though the entire examination apparatus including the reception antenna is surrounded by a high-frequency shielded chamber. One cause of this disturbance is believed to be partial discharges at the gradient coils, which occur particularly when the coils are charged with signals (pulses) having steep edges in the chronological curve which defines the gradient fields. Partial discharges can particularly occur given low atmospheric humidity in the examination space. Heretofore, if a tomographic image was obtained in which such artifacts were present, the only recourse was to repeat the measurement sequence so as to obtain a new tomogram.